Non-supported, fixed bed catalyst pellets are used in many chemical processes. Among these are processes for dehydrogenation, hydrogenation, and oxidation of organics. Dehydrogenation processes using such fixed bed, non-supported catalysts include the dehydrogenation of ethylbenzene to produce styrene, of ethyl toluene to produce vinyl toluene, and of butane or butene to produce butadiene.
Hydrogenation processes which use such fixed bed, non-supported catalysts include such processes as that for producing saturated hydrocarbons from olefins.
Oxidation processes which use such fixed bed, non-supported catalyst pellets include such processes as those for making aldehydes and acids from saturated and unsaturated hydrocarbons, e.g. acrylic acid from propylene.
For the sake of conciseness, the word pellets is hereinafter used as a generic term to include those spray dried tablets made by the process of this invention as well as other forms of pellets made by such processes as extrusion, i.e., extrudates. Tablet is defined to be any pellet made by the process of this invention.
In the past, improvements in the catalytic performance and/or crush strength of non-supported catalyst pellets for the processes referred to above, have generally been obtained by changing the formulation of components. Typically such non-supported catalyst pellets are made by extruding a paste of components through cylindrical dies to form moist cylinders having a diameter of from about 1/16 inch to about 1/2 inch. As these cylinders exit from the extruder they are usually either chopped into predetermined lengths or allowed to break of their own weight, forming cylindrical pellets (extrudates) having a length of from about 1/8 inch to about one inch.
Methods other than extrusion have been taught for forming non-supported catalyst pellets. For example U.S. Pat. No. 1,680,807 (Aug. 14, 1928) teaches the formation of catalyst tablets by compression of a multiplicity of fine particles of catalytic material, which particles are not naturally coherent in the dry state. Spray drying of fluid bed catalysts is known. See U.S. Pat. Nos. 2,768,145 (Tongue et al. 1956) and 1,680,807 (Scultze 1928). Spray drying catalyst materials on catalyst carriers or supports is known. See U.S. Pat. No. 2,435,379 (Archibald 1948).
The process of the present invention, however, comprises the combination of the steps of (1) spray drying a slurry of catalyst source constituents into microspheres, and (2) forming at least one tablet from these microspheres by subjecting them to large compressive forces, such as tabletting in a punch and die set. For some unknown reason this combination of steps produces a catalyst tablet having superior catalytic performance and/or crush strength qualities.
It should be noted that the phrase "a slurry of catalyst source constituents" is used above in the spray drying step as opposed to "a slurry of catalyst components". This is done to point out that sometimes the constituents used in making up the slurry for spray drying are not the same components as those found in the final formulation of the catalyst tablets to be used. Often after adding the constitutents together, or in subsequent steps in making the catalyst pellets, chemical changes occur in these constituents. Thus different constituents other than those started with often appear in the final catalyst pellet formulation. Of course, there are also catalyst slurry formulations which are not changed. This invention is applicable to both. Hence, as used hereinafter the phrase "catalyst source constituents" is defined to mean not only those constituents which appear in one form in the slurry and another form in the finished catalyst tablet, but also to those constituents that appear in the same form in both the slurry and the finished tablet. For example K.sub.2 CO.sub.3 is a source for K.sub.2 O if the K.sub.2 CO.sub.3 is converted to K.sub.2 O. Also K.sub.2 O itself is source of K.sub.2 O by this definition.